The millionaire writer, 37, is believed to be three months pregnant.

A spokeswoman said: "JK Rowling and Dr Neil Murray are delighted to confirm that they are expecting a baby in the spring."

The second Harry Potter film is released in November

The writer has a nine-year-old daughter, Jessica, from a previous marriage.

Rowling married Dr Murray in a secret Boxing Day ceremony last year at the writer's home in Perthshire, Scotland.

The ceremony was a reportedly low-key affair, attended only by immediate family members and close friends.

Her daughter Jessica was one of three bridesmaids.

'Publishing phenomenon'

Her first marriage was to Jorges Arantes, a Portuguese journalist whom she met while working in Portugal.

They later divorced and she returned to Edinburgh.

The author famously wrote the first of the Harry Potter novels as she sat in a local cafe, Nicolson's.

Rowling's tales of the boy wizard's exploits have become a publishing phenomenon, gripping millions of children and adults around the world.

She has promised fans who have been waiting two years for the fifth instalment that Harry Potter and the Order of the Phoenix is not too far away, and that she is just in the process of "tweaking" it.

Plagiarism victory

She has just won a court battle against a US writer who claimed she had stolen ideas for Harry Potter.

Pennsylvania-based writer Nancy Stouffer claimed Rowling had lifted ideas from her own book The Legend of Rah and the Muggles and wanted to be recognised as Harry Potter's creator.

But a court in New York threw out the claim for plagiarism against Rowling, US publisher Scholastic and film producers Warner Bros, ruling Ms Stouffer had lied and altered documents to support her case.

Ms Stouffer was fined $30,000 (£19,363) for this "pattern of intentional bad faith conduct" and ordered her to pay a percentage of the defendant's costs.

Meanwhile, Harry Potter's two-and-a-half year reign at the top of the children's best-selling paperbacks list has ended.

The books have taken it in turns to top the chart, compiled by Nielsen BookScan, continuously since they were published.

However the fourth book, Harry Potter And The Goblet Of Fire, has now been knocked from pole position by Princess Diaries 4: Mia Goes Fourth by American writer Meg Cabot.

The Princess Diaries series follows the adventures of a New York teenager who becomes crown princess of a European principality.

A film of the first book was released last year.